Centrifugally armed fuze for rotating projectile



lNVE/VTUR w/um/v GUEP/VE w. GUERNE CENTRIFUGALLY ARMED FUZE FOR ROTATING PROJECTILE Original Filed April 21, 1958 Feb 5 1963 ATTORNEY 3,076,410 CENTRIFUGALLY ARMED FUZE FOR ROTATING PROJECTILE William Guerne, Geneva, Switzeriand, assignor to Brevets Aero-Mecaniques S.A., Geneva, Switzerland, a Swiss society Continuation of application Ser. No. 729,921, Apr. 21,

1958. This application Nov. 25, 1960, Ser. No. 71,575 Claims priority, application Luxembourg Apr. 25, 1957 6 Claims. (Cl. 102-79) This application is a continuation of application Serial No. 729,921 filed April 21, 1958, and now abandoned.

This invention relates to centrifugally-armed fuzes for rotatable or spin stabilized projectiles, -i.e. to fuzes wherein the striker or like igniting means is normally retained at the inoperative position by a locking device and is liberated under the action of centrifugal forces developed by rotation of the projectile when the latter is fired, whereby the fuze is armed, as for instance by being rendered sensitive to impact.

In the conventional centrifugally-armed fuzes the locking device is liberated as soon as the projectile begins rotating about its axis at a sufficient angular velocity. Consequently the fuze is armed immediately at the outlet of the gun or even within the latter and the projectile is therefore liable to burst on impact against any kind of unexpected object, such as for instance branches, wires, etc.

The present invention has for its object to provide a fuze wherein the arming of the fuze is delayed.

In accordance with this invention in a centrifugallyarmed fuze the locking device is rotatable with respect to the fuze about the axis thereof and is submitted to the temporary action of means which under the action of centrifugal forces cause the said locking device to rotate during a time with respect to the fuze in a direction opposed to the direction of rotation of the fuze itself and at such a relative angular velocity that the absolute angular velocity of the said device about the fuze axis be temporarily lowered below the minimum value for which the said device liberates the striker or like igniting means.

The locking device is conveniently in the form of a split expansible sleeve loosely mounted on the striker or the like and adapted to form a retaining abutment for a shoulder thereof before the projectile is launched, means being provided to frictionally connect the said sleeve and the body of the fuze while permitting angular slip.-

The sleeve may be retained against expansion by the means adapted to rotate the said sleeve with respect to the fuze itself during the operating step of the said means.

The means adapted to rotate temporarily the sleeve within the fuze body when the projectile is fired may be I in the form of a strip, preferably made of a resilient or non-resilient metal such as tin, the said strip being wound about the sleeve an appropriate number of times and its inner end being attached to the sleeve, while its outer end is secured to the fuze body, at least when the projectile is tired, the winding direction of the said strip about the said sleeve being such that when the said strip unwinds under the action of centrifugal forces, the sleeve be rotated in-the fuze in the reverse direction with respect to the direction of rotation of the projectile.

Before the projectile is fired the strip is tightly wound on the sleeve and it is conveniently surrounded by a safety split ring, which opens under the action of centrifugal forces, whereby the outer end of the strip may apply against the fuze body and become frictionally secured thereto by the said forces.

The inner end of the strip may be disengageably anchored onto the sleeve at two points situated on each side of the slot thereof, in such a manner that the said sleeve is retained against expansion under the action of centrifugal forces until the said strip is wholly disengaged therefrom. For this purpose the sleeve may be formed with two anchoring notches on each side of its slot, the strip being pressed and engaged into the said notches.

In the annexed drawings:

FIG. 1 is a sectional elevation of a fuze according to this invention. 1

FIG. 2 is an enlarged transverse section thereof taken along line :IIII of FIG. 1.

In the annexed drawings reference numeral 1 designates a striker slidably disposed in the body 2 of the fuze, the said striker being adapted to move rearwardly within the fuze on impact to cause ignition of a pyrotechnic composition such as for instance an initiating charge or primer, disposed in the bottom of the fuze body 2.

Until the projectile on which the fuze is mounted is fired, striker 1 is retained at an advanced position within the fuze body by means of a locking device adapted to be thereafter released by centrifugal forces developed by rotation of the projectile about its axis when it has been launched. In the example illustrated this locking evice is formed of a radially split and therefore expansible sleeve 4 which, until the projectile is fired, forms an abutment for a shoulder 1a provided on striker 1. -As illustrated this split sleeve 4 is of substantial width. It is provided with a radial slot 4a opening at both ends and with a number of additional notches 4b, 40 which do not extend to the inner surface of the said sleeve, these notches increasing the flexibility of the sleeve.

With the above-described arrangement the split expansible sleeve 4 would expand as soon as the angular velocity of the projectile about its own axis exceeds a predetermined value. In other Words the fuze would become armed at its outlet from the gun or even within the latter. The projectile could therefore burst on impact against branches, camouflage c'ontrivances, etc., or even due to a plug of grease left at the outlet of the gun.

According to the present invention this is avoidedby so mounting the expansible locking sleeve 4 that when the projectile is fired, the said sleeve may rotate with respect to the fuze about the axis of the latter and by providing centrifugal means whereby the sleeve is then caused to rotate temporarily with respect to the fuze in the reverse direction with respect to the direction of rotation of the fune itself, in such a manner that theabsolute angular velocity of the sleeve is then smaller than the angular velocity of the fuze and remains below the limit required to liberate striker 1, when the aforesaid centrifugal means become ineffective, the angular ve; locity of sleeve 4 tends to increase under the action of frictional forces until it is equal to the angular velocity of the fuze itself. The sleeve therefore expands and liberates the striker, whereby the fuze is armed. In other words the arming of the fuze is delayed, whereby the latter is safe against untimely operation on a given leng temporarily rotate the expansible sleeve 4 that they positively retain the sleeve at its unexpanded position during their rotating action on the latter. With such an arrangement the fuze remains safe even, for instance, if the absolute angular velocity of the expansible sleeve 4 after the projectile has just been fired is somewhat higher than provided, or if the expansible sleeve is somewhat more flexible than expected.

lnthe illustrated embodiment thisis obtained by winding on the expansible sleeve 4 a strip preferably made of a resilient or non-resilient metal, such as tin, for instance. This"win'ding may comprise 'a pre-det'errnined number of turns, "as for instance about twelve. The inher end I of'strip 5 is anchored onto "sleeve 4, 'while its outerend Eis adapted to be secured to the fuze body 2, either in a permanent manner, or under the action of centrifugal forces when the projeetile is launched, as hereinafter explained. The direction of winding of strip 5 about striker 1 is such that when the projectile rotates, the unwinding "of the successive turns 'of the said strip under the action of centrifugal forces should rotate the "expansible sleeve 4 ab'outstriker 1 with respect to the fuze in a direction opposite to the direction of rotation of the fuze about its own axis. In FIG. 2 arrow F indica'testhe direction of rotation of the fuze, while arrow indicates the direction of the relative r'otation of the sleeve within the fuze.

Thes't'rip 5 wound on the striker 1 is preferably norfinally retained in position by an outer split ring 6 which s ans under the action of centrifugal forces as soon as the projectile begins rotating, as shown in FIG. 2. The outer end of strip '5 is then liberated and it is applied by centrifugal forces against the outer wall of an annular reeess 7 provided in the fuze body around the cylin- "drioalportion' of'striker 1 on which 'the'expansible-sleeve Wis disposed. The inner end I of strip Sis preferably anchored onto the split iexpansimesneve 4 at two pointsdisposed on 'e'a'clrside of the'slot "4a thereof in such a manner that "the portion of the "strip "extending between these points and which bridges the said slot 4a may retain the sleeve in the unexpfanded state until the strip is wholly unwound therefrom. In the example illustrated this is "obtained by means of the above mentioned notches "4b which are disposed on each'side 'of the slot 4a of the sleeve, "strip '5 being pre'ssed into the said notches by means of 'an appropriate tool which forms thereon depressions "5b which fit into the said notches 4b. As above"explain'ed notches 4b cooperate with notches '4c 'for increas n the flexibility and therefore the expansibility of-"sleeve '4.

It will be appreciated that the safety delay between the launching of the projectile and the arming of the f'fu'ze is dependent of anumber of factors, such as the j thicknes's "of strip '5, the length thereof, the mass of "sleeve 4, etc. The thickness of strip is preferably as 'fe'duee'd as '-possible in order that the said strip may easily break, should the depressed portions thereof betameammed within notches 4b "at theend of thennwindin'g step. ;It"is besides 'of interest'to have the *said etriprelatively as long as the radial dimension of the annular amusing 7 will permit in order -'to "increase the safety delay. When the strip is fully unwound, the "'s eeve4"'is progressively brought to rotate at the "same, absolute angular velocity as the fuze by the frictional 'fore's and 'of 'course the time required therefore is' m'ore Tor-less "p'roport'iorial to the mass of the sleeve or, more exactly, to its moment of inertia about the axis of the rare.

The ger'ieral operation *of the fuz'e is now' clearly' un- "derstairdaljlez As soon as the projectile is fired, it rotates at a high speed about its axis in the direction indicated by the an raw-F in FIG. 2. During the accelerating step within the "gun, "the safety ring 6 is strongly applied against "the'infne'r 'or fron't'side of the plug which forms the "rear -part of thefuze and it therefore rotates-substantially at the "same angular velocity as the projectile. 'It is consequently almost-at once expanded and applied against the;outer wall of the annular housing 7 'under the-action of centrifugalforces. The outer end of strip 5 is consequently liberated and it is urged outwardly bycentri-fugal forces and also applied against the outer wall of'housing '7, or against the inner side of the expanded ring 6, as illustrated in FIG. 2. The successive portions of the strip are in turn urged outwardly and the said strip thus tends to unwind from striker 1 for becoming wound internally against the outer wall of housing 7.

But owing to the difference in diameter between sleeve '4 and the outer wall of housing 7, this kind of transfer of strtip -5 from the sleeve to the said outer wall involves a relative rotation between the ends I and E of the strip. Now the outer end E 'is already strongly applied against the aforesaid outer wall "by centrifugal forces and 'it is frictionally retained 'or "secured thereon. As 'to the inner end I, it is anchored onto sleeve 4 as above explained, and the said sleeve is strongly pressed against the plug or rear end of the fuze by the inertia forces which result from the accelerationof the projectile within the gun, the said forces also acting on the striker 1 itself, the shoulder 1a of which is therefore strongly applied against the front end of the sleeve. Strip 5 is therefore prevented from unwinding until the projectile has left the-gun. Sleeve '4 is then free to rotate on striker 1 and strip '5 may unwind from the said sleeve, the latter rotating in the direction of arrow f of FIG. 2, Le. in the reverse direction with respect to 'the rotation of the projectile. The absolute angular velocity of the sleeve is therefore equal'to the difference between the angular velocity of the projectile-and the relative angular velocity of the said sleeve with respect to the fuze. Since the'unwinding of the strip is a rather rapid proc ess, this absolute angular velocity of sleeve 4 is relatively low and it may even be quite nil. In any case, it is insufficient for causing expansion of the sleeve. When the strip is wholly unwound from the sleeve, its depressed portions 5b which had been driven into notches 4b are disengaged, thus leaving sleeve '4 quite free. Under the action of frictional forces the latter tends to assurne progressively the same angular velocity as the fu'ze itself, whereby it is expanded by centrifugal forces. Striker l'isthen free to "act on impact or-in other words the fuzeis armed.

It willbe noted "that even if for any'reason sleeve 4 had some tendency to expand before the 'final unwinding of the *strip, it would be positively prevented from doing so by the-portion of the said strip which bridges the slot 4a of the sleeve and which is anchored-onto the said sleeve at both'end's in notches 4b.

What I claim -1.--A centrifugally-arined fuze for a rotatable projectile comprising a fuze body formed with an axial bore and with anaxially substantially cylindrical'inner housing having 'alateral wall, a transverse front wall and a transverse rear wall, a charge tobe ignited disposed substantially at the rear end of said axial bore, a striker slidably disposed within said bore to cause ignition of said charge by moving 'rearwardly of said fuze from an advanced position to a rear'position, said striker being forrned'with a shoulder'situated in front of the rear wall of said-housing whensaid striker is at its advanced position, and with a'cylindrical portion disposed at the rear of said shoulder, a cntrif-ugally expansible split sleeve 'frely'i and -'rotatably mounted on said cylindrical portion'between'said shoulder and the rear wall of said housing to retain said striker at its advanced position, a flexible'strip'spiral wound on 'said sleeve in the reverse 'direction with respect'to the rotation of said projectile when fired, said strip having its inner end attached to said sleeve, anda centrifugally expansible ring disposed on said flexible strip to retain same on said sleeve until the projectile 'is"fired,-rotationof the latter then causing expansion of said ring which liberates said flexible-strip, and the outer end of said strip then being applied by centrifugal force against the outer wall of said housing whereon it is'frictionally secured to cause said strip to rotatesaidsplitsleeve within said fuze body in the reverse direction with respect to the rotation of said fuze.

2. In a fuze as claimed in claim 1 the inner end of said flexible strip bridging the split portion of said sleeve and being disengageably anchored onto said sleeve each side of said split portion to retain said sleeve at the unexpanded position on said cylindrical portion of said striker until said strip is fully unwound and disengaged from said sleeve.

3. In a fuze as claimed in claim 1, said split sleeve being formed with a peripheral notch on each side of the split portion thereof and the inner turn of said flexible strip being formed with depressions forced into said notches to cause the portion of said inner turn which extends between said notches to retain said sleeve at the unexpanded position on said cylindrical portion of said striker until said depressions are disengaged from said notches at the end of the centrifugal unwinding of said strip from said sleeve.

4. In a projectile fuze armed by rotation of the projectile to unwind centrifugally a flexible strip wound spirally about a centrifugally releasable split sleeve interposed between a shoulder portion of ignition means and an explosive charge toward which the ignition means is relatively movable, means for releasably securing the flexible strip to the split sleeve including at least one notch disposed in the outer peripheral portion of the split sleeve adjacent each side of the split, the flexible strip being indented into each of the notches and so wound about the split sleeve as to rotate the split sleeve temporarily in the opposite direction from that of the projectile, such that centrifugal release of the split sleeve is delayed.

5. A projectile fuze according to claim 4 further cornpn'sing a centrifugally releaseable safety ring wound about the flexible strip.

6. A centrifugally armed fuze for a rotatable projectile comprising a fuze body formed with an axial bore and with an axially disposed inner housing having a transverse wall fixed in the axial direction, igniting means comprising two elements, one fixed with respect to said fuze body and the other movable axially in said bore in response to impact of the projectile on an obstacle to cause ignition by moving in the axial direction of said fuze from a first position where it is at a distance from said fixed element to a second position where it is in contact with said fixed element, said movable element being formed with a shoulder portion capable of moving in said housing and the axial distance of which from said housing transverse wall decreases when said movable element moves from said first position to said second position, an expansible split sleeve freely and rotatably interposed around said movable element between the shoulder portion thereof and said housing transverse wall to retain said fixed element in its first position, and a flexible strip having an inner end attached to said split sleeve and spiral wound about it in a direction such as to rotate it initially in the opposite direction from that of the projectile, whereby centrifugal release of the split sleeve is delayed.

References Cited in the file of this patent UNITED STATES PATENTS 2,715,873 Thompson Aug. 23, 1955 2,790,390 Baker Apr. 30, 1957 2,873,678 Koonz Feb. 17, 1959 FOREIGN PATENTS 61,219 Denmark July 26, 1943 

6. A CENTRIFUGALLY ARMED FUZE FOR A ROTATABLE PROJECTILE COMPRISING A FUZE BODY FORMED WITH AN AXIAL BORE AND WITH AN AXIALLY DISPOSED INNER HOUSING HAVING A TRANSVERSE WALL FIXED IN THE AXIAL DIRECTION, IGNITING MEANS COMPRISING TWO ELEMENTS, ONE FIXED WITH RESPECT TO SAID FUZE BODY AND THE OTHER MOVABLE AXIALLY IN SAID BORE IN RESPONSE TO IMPACT OF THE PROJECTILE ON AN OBSTACLE TO CAUSE IGNITION BY MOVING IN THE AXIAL DIRECTION OF SAID FUZE FROM A FIRST POSITION WHERE IT IS AT A DISTANCE FROM SAID FIXED ELEMENT TO A SECOND POSITION WHERE IT IS IN CONTACT WITH SAID FIXED ELEMENT, SAID MOVABLE ELEMENT BEING FORMED WITH A SHOULDER PORTION CAPABLE OF MOVING IN SAID HOUSING AND THE AXIAL DISTANCE OF WHICH FROM SAID HOUSING TRANSVERSE WALL DECREASES WHEN SAID MOVABLE ELEMENT MOVES FROM SAID FIRST POSITION TO SAID SECOND POSITION, AN EXPANSIBLE SPLIT SLEEVE FREELY AND ROTATABLY INTERPOSED AROUND SAID MOVABLE ELEMENT BETWEEN THE SHOULDER PORTION THEREOF AND SAID HOUSING TRANSVERSE WALL TO RETAIN SAID FIXED ELEMENT IN ITS FIRST POSITION, AND A FLEXIBLE STRIP HAVING AN INNER END ATTACHED TO SAID SPLIT SLEEVE AND SPIRAL WOUND ABOUT IT IN A DIRECTION SUCH AS TO ROTATE IT INITIALLY IN THE OPPOSITE DIRECTION FROM THAT OF THE PROJECTILE, WHEREBY CENTRIFUGAL RELEASE OF THE SPLIT SLEEVE IS DELAYED. 